1. Field of the Invention
The present invention relates to a data processing apparatus, a data erasing method therefore, and a program for implementing the method.
2. Description of the Related Art
Conventional image forming apparatuses (data processing apparatuses) are configured such that copying or printing stops when shutdown of commercial power supply such as a power failure or an instantaneous interruption over a relatively long period of time occurs in the image forming apparatus. Then, irrespective of the type of a job being processed at a time point the power shutdown occurred, print data generated by the job remains as incomplete data in a storage medium such as a hard disk. As a result, when power supply to the image forming apparatus is turned on next time, the incomplete data remaining in the storage medium is regarded as improper data. Then, the image forming apparatus erases related table data such as FAT (File Allocation Table) to cut off the relationship with the print data.
Also, when a power shutdown occurs while print data is being stored in a HD (hard disk) in the image forming apparatus, a sector or sectors in the HD become bad during writing. Then, when power supply to the image forming apparatus is turned next time, there is the possibility that the sector/sectors is/are unusable as bad sector(s). To cope with this, it can be envisaged that the voltage supply is switched from a normally used DC power supply to a backup power supply when a power shutdown occurs.
On the other hand, there has been known an image forming apparatus that is capable of executing a print job with a password for improvement of security (hereinafter referred to as “the secure job”) as well as a normal print job (hereinafter referred to as “the normal job”). The secure job comprised of transmitting print data to which a password that can be set with respect to each user is added from an external apparatus such as a personal computer to the image forming apparatus, so that the secure job is not printed out insofar as a user directly enters the password from the image forming apparatus.
Further, there has been proposed a technique that can properly cope with a request to immediately shut down power supply without causing any serious problems even in the case where a power switch is unexpectedly turned off by a user. According to this technique, when an operation detecting section detects power shutdown, the power supply is switched to a backup power supply, so that data on a RAM is transmitted to an external apparatus via a network or data is saved from a volatile storage device in a nonvolatile storage device, and then the power shutdown is notified (see Japanese Laid-Open Patent Publication (Kokai) No. 2004-072711, for example).
In the above conventional image forming apparatus, however, irrespective of whether a job to be executed by the image forming apparatus is the secure job or the normal job, the same process is carried out upon abnormal power shutdown in which power supply to the image forming apparatus is abnormally shut down. That is, when an abnormal power shutdown occurs, the image forming apparatus determines that print data being processed is improper data in the same manner as mentioned above. When the supply of voltage to the image forming apparatus is resumed, the image forming apparatus erases related table data such as FAT.
Once an abnormal power shutdown occurs in the image forming apparatus, the image forming apparatus cannot be caused to execute the secure job even if a user who has input the secure job from an external apparatus such as a personal computer (PC) attempts to enter a password to the image forming apparatus, because the image forming apparatus pauses due to the cutoff of power supply thereto. The user is very concerned about the location of the print data that has been completely transmitted from the PC to the image forming apparatus, which raises a problem in terms of security.
There are the following job processing statuses in the image forming apparatus when an abnormal power shutdown occurs.
(1) The status as to whether or not a print data job input from a PC is being processed
(2) The status as to progress of job processing in the case where the job is being processed
(2-1) The status as to storage of PDL data in a receiving buffer in the image forming apparatus
(2-2) The status as to creation of various bitmap data by generating a drawing command list from the PDL data
(2-3) The status as to spooling of the bitmap data that has been completely drawn
In the above conventional image forming apparatus, however, the method of handling print job data being processed when an abnormal power shutdown occurs is not variable at any of the job processing stages mentioned above. Thus, there is the disadvantage that if bitmap data that has been completely drawn remains in the HD of the image forming apparatus as it is or in a compressed form, a third party can maliciously steal a look at and parse the data.
Also, even the image forming apparatus that employs the switching method in which the power supply is switched from a DC power supply to a backup power supply when an abnormal power shutdown occurs, it is a matter of course that the residual power supply capacity of the backup power supply decreases as the operating time of the backup power supply increase. However, since the system terminating process to be carried out in response to abnormal power shutdown is not variable so as to cope with changes in the power supply capacity of the backup power supply, the residual power supply capacity of the backup power supply cannot be effectively used because it is limited by the system terminating process to be carried out.